1. Field of the Invention
The invention relates to a method for the common transmission of digital source data and control data between data sources and data sinks, which are subscribers to a communication network with a ring structure, the source data and control data being transmitted in a format which prescribes a pulsed sequence of individual bit groups of identical length in which specific bit positions are reserved in each case for source data and control data, which are transmitted in a continuous data stream synchronous with a clock signal. The clock signal is generated by a single subscriber. All other subscribers are synchronized with this clock signal. Data transmission methods which are purely packet orientated such as, for example, the ATM method, i.e., asynchronous transfer methods, are to be distinguished from these. The invention is also directed towards specific applications of the novel method in a domestic communication system and a communication system for motor vehicles.
Methods of this type are used wherever electric and electronic devices of different types which are intended to exchange information with one another are mutually networked, often in a complicated way, by means of data lines. Thus, for example, in audio applications such a method can be used to control communication between mutually networked data sources, on the one hand, such as CD players, radio receivers and cassette recorders, for example, and data sinks connected thereto, on the other hand such as, for example, amplifier/loudspeaker combinations. Certain devices can thereby be a data source and a data sink (e.g. cassette recorder/player).
2. Description of the Related Art
It has become known heretofore from European patent disclosure EP-A-0 725 522 to interconnect different types of network subscribers by optical fibers in such a way that the data stream passes each subscriber sequentially. An optical communication network with a ring structure is then produced which has particular advantages, in particular for mobile applications, for example in motor vehicles, and domestic applications, for example in multimedia networks. In order to be able to transmit data between a multiplicity of interconnected subscribers in such a network, the positional region within a bit group which is reserved for the source data transmitted in a continuous data stream can be subdivided into a plurality of component bit groups of identical length. It is thereby possible for the source data allocated to each component bit group to be assigned to a specific subscriber as a function of the control data. The component bit groups form channels which are available in each case to a specific subscriber for an unspecified time.
Data transmission in a data stream synchronous with a clock signal, as it is typical of the methods mentioned, permits simple connection to data sources and data sinks, which likewise transmit and receive continuously. This is the case with many audio and video devices, for example. In addition, the current quality requirements in the audio field, for example, can be met with acceptable outlay generally only given synchronous data transmission.
In principle, those methods can also be used to transmit data which originate from a device which supplies data in an asynchronous mode such as, for example, a fax machine or a CD-ROM drive. It is necessary for that purpose to synchronize the data delivered in bursts with the clock signal, and to transmit the synchronized data via a channel which is formed by specific bit positions and is assigned to the receiver of the data. During the time in which it is assigned to the receiver, the channel is not available for any other data. Since the assignment and rerelease of channels takes a relatively long time, a substantial amount of transmission capacity is sacrificed. Further transmission capacity is sacrificed by short gaps between individual bursts, which do not permit a channel release in the meantime.
The above-noted EP-A-0 725 522 proposes to transmit fax data or other unformatted, i.e., uncoded, data via so-called transparent channels which are provided in the regions reserved for the control data. These channels, however, are then available only for a very specific purpose, and the above-mentioned disadvantages are encountered. Again, the transmission capacity of the permanently reserved transparent channels is limited by virtue of the system.